
using System;

namespace Poc1.Universe.OpenGl
{
	/// <summary>
	/// Simple un-optimised noise, nabbed from Ken Perlin's java implementation
	/// </summary>
	public static class SimpleNoise
	{
		/// <summary>
		/// Returns a noise value given the input value x
		/// </summary>
		public static float Noise( float x )
		{
			int iX = ( int )x;
			return NoiseBasis( iX ) / 2 + NoiseBasis( iX - 1 ) / 4 + NoiseBasis( iX + 1 ) / 4;
		}

		/// <summary>
		/// Returns a noise value given the input position (x,y,z). 
		/// </summary>
		/// <param name="x"></param>
		/// <param name="y"></param>
		/// <param name="z"></param>
		/// <returns>Noise value in the range [-0.5f,0.5f]</returns>
		public static float Noise( float x, float y, float z )
		{
			int X = ( int )Math.Floor( x ) & 255,                  // FIND UNIT CUBE THAT
				Y = ( int )Math.Floor( y ) & 255,                  // CONTAINS POINT.
				Z = ( int )Math.Floor( z ) & 255;
			x -= ( float )Math.Floor( x );                                // FIND RELATIVE X,Y,Z
			y -= ( float )Math.Floor( y );                                // OF POINT IN CUBE.
			z -= ( float )Math.Floor( z );
			float u = fade( x ),                                // COMPUTE FADE CURVES
				   v = fade( y ),                                // FOR EACH OF X,Y,Z.
				   w = fade( z );
			int A = p[ X ] + Y, AA = p[ A ] + Z, AB = p[ A + 1 ] + Z,      // HASH COORDINATES OF
				B = p[ X + 1 ] + Y, BA = p[ B ] + Z, BB = p[ B + 1 ] + Z;      // THE 8 CUBE CORNERS,

			return lerp( w, lerp( v, lerp( u, grad( p[ AA ], x, y, z ),  // AND ADD
										   grad( p[ BA ], x - 1, y, z ) ), // BLENDED
								   lerp( u, grad( p[ AB ], x, y - 1, z ),  // RESULTS
										   grad( p[ BB ], x - 1, y - 1, z ) ) ),// FROM  8
						   lerp( v, lerp( u, grad( p[ AA + 1 ], x, y, z - 1 ),  // CORNERS
										   grad( p[ BA + 1 ], x - 1, y, z - 1 ) ), // OF CUBE
								   lerp( u, grad( p[ AB + 1 ], x, y - 1, z - 1 ),
										   grad( p[ BB + 1 ], x - 1, y - 1, z - 1 ) ) ) );
		}

		#region Private Members

		private static float fade( float t )
		{
			return t * t * t * ( t * ( t * 6 - 15 ) + 10 );
		}

		private static float lerp( float t, float a, float b )
		{
			return a + t * ( b - a );
		}

		private static float grad( int hash, float x, float y, float z )
		{
			int h = hash & 15;                      // CONVERT LO 4 BITS OF HASH CODE
			float u = h < 8 ? x : y,                 // INTO 12 GRADIENT DIRECTIONS.
				   v = h < 4 ? y : h == 12 || h == 14 ? x : z;
			return ( ( h & 1 ) == 0 ? u : -u ) + ( ( h & 2 ) == 0 ? v : -v );
		}

		private static readonly int[] p = new int[ 512 ];
		private static readonly int[] permutation = new int[]
		{
			151,160,137,91,90,15,
			131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142,8,99,37,240,21,10,23,
			190, 6,148,247,120,234,75,0,26,197,62,94,252,219,203,117,35,11,32,57,177,33,
			88,237,149,56,87,174,20,125,136,171,168, 68,175,74,165,71,134,139,48,27,166,
			77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41,55,46,245,40,244,
			102,143,54, 65,25,63,161, 1,216,80,73,209,76,132,187,208, 89,18,169,200,196,
			135,130,116,188,159,86,164,100,109,198,173,186, 3,64,52,217,226,250,124,123,
			5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182,189,28,42,
			223,183,170,213,119,248,152, 2,44,154,163, 70,221,153,101,155,167, 43,172,9,
			129,22,39,253, 19,98,108,110,79,113,224,232,178,185, 112,104,218,246,97,228,
			251,34,242,193,238,210,144,12,191,179,162,241, 81,51,145,235,249,14,239,107,
			49,192,214, 31,181,199,106,157,184, 84,204,176,115,121,50,45,127, 4,150,254,
			138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180
	   };

		/// <summary>
		/// Sets up permnutation and index tables for 3-valued noise
		/// </summary>
		static SimpleNoise( )
		{
			for ( int i = 0; i < 256; ++i )
			{
				p[ 256 + i ] = p[ i ] = permutation[ i ];
			}
		}

		/// <summary>
		/// Basis function for single-valued noise
		/// </summary>
		private static float NoiseBasis( int x )
		{
			uint n = ( uint )( x );
			n = ( n << 13 ) ^ n;
			return ( 1.0f - ( ( n * ( n * n * 15731 + 789221 ) + 1376312589 ) & 0x7fffffff ) / 1073741824.0f );
		} 
		#endregion

	}
}
